design purposed of rain water harvesting system at roof level

8/3/2019 Design Purposed of Rain Water Harvesting System at Roof Level

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DESIGN PURPOSED OF RAIN WATER HARVESTING SYSTEM AT ROOF

LEVEL

CALCULATION OF BEAM

CALCULATED BY: AYUB SAIDI

DATA:

Slab thickness: 200mm

Finishes: 1.0 Kn/m2

Live load (qk): 7.5 KN/ m2 (Base on table 8, BS 6399: pt1:

1984)

Exposure Condt. Mild

Fcu: 30 N/mm2

Fy: 460 N/ mm2

Self weight of slab

0.2m X 24 KN/m3 = 4.8 KN/ m2

Load due to finishes

10 KN/ m2

Load due to imposed load

7.5 KN/ m2

Ultimate Design Load

1.4 gk + 1.6 qk = (1.4(5.8) + 1.6(7.5)) = 20.12 KN/ m2

For beam C.A/1-2 = Beam C.A/2-3

Load from slab, 2 way slab action base on calculation ly/lx;

Ly/lx = 5.2/4.6 =1.13 < 2.0 ( 2 way slab)


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At beam C.A / 1-2

Each trapezium area;

5.182+0.582X 2.3 X 20.12 KN/ m2 = 133. 32 KN

2 X 133.32 KN = 266.64 KN

At end of beam, point load equal to 133.32KN each

At beam 2/C-D

Each triangle acting on it equal to

4.62 X 2.3 X 20.12 KN/ m2= 106.43 KN

4 X 106.43 KN = 425.72KN/ 9.2 m = 46.27 KN/m

Primary Beam size (600 X 225)

Self weight of beam = (0.6 X 0.23 X 24) = 3.312 KN/m

Design load = 1.4 X 3.312 KN/m = 4.64 KN/m

Add to existing load; 46.27 + 4.64 = 50.91kn/m

Hence for beam 2/C-D, all load acting on it is

Design on beam 2/C-D

Maximum bending moment

WL82 +

PL4 = 538.63 + 306.64 = 845.27 KN.M

K = M/ fcubd2

Assume main bar and cover = 25 mm, d = 600 - 25 - (25/2) =

562.5 mm

845.27 X 106 / 30 X 225 X 562.52 = 0.396 > 0.156 (doubly

reinforcement)


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Z = d ( 0.5 + 0.25-k/0.9 ) = 562.5 ( 0.5 + 0.25-0.396/0.9 )

= 528.75

Area of compression reinforcement (As)

As = (k-k) fcubd2 / 0.95 fy (d-d)

Assume diameter of compression bar = 25 mm

d = cover + diam eter of bar/2 = 37.5mm

As = (0.396-0.156) 30X225X562.52 / 0.95X460X(562.5-37.5)

= 2234.6 mm2, provide 5T25 (2450 mm2)

Area of tension reinforcement (As)

As = M/ 0.95fyz = 845.27 X 106 / 0.95X460X528.75

= 3658.17 mm2, provide 8T25 (3930 mm2)

Since the new load to resist is massive in number, we have to

check if this new load can be resist by the existing beam

structure in this area.

Deflection check

Actual, span/d = 9200/ 562.5 = 16.36

Permissible;

Fs = 2/3 X fy X (As req/ As Prov)

= 2/3 X 460 X (3658.17 / 3930 ) = 285.45

Modification factor;

= 0.55 + [(477 Fs)/ 120 (0.9 + m/bd2 )], m/bd2 = 11.87

0.55 + [0.125] = 0.675

Thus, L/d basic(simply supported) = 20

l/d allow = 0.675 X 20 = 13.5 < 16.36

(The deflection is unacceptable)

Further calculation cant be made because the deflection

criteria is not acceptable. To counter this measure, we can

suggest that we have to provide deeper concrete section for

this beam. Further calculation was made for beam 1 / C-D and

still the result is just the same. Since the existing structure

cant be alter and resist the load, we decide not to design the

rainwater harvesting system in this building.


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design purposed of rain water harvesting system at roof level

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